CVE-2026-40539: Improper Cert Validation in Synology DSM Email API (pre-7.2.1)
CVE-2026-40539 Published on September 18, 2026
An improper certificate validation vulnerability in Email API in Synology DiskStation Manager (DSM) before 7.2.1-69057-10, 7.2.2-72806-7 and 7.3.2-86009-2 allows man-in-the-middle attackers to read or write arbitrary files and conduct denial-of-service attacks.
Vulnerability Analysis
Weakness Type
Improper Certificate Validation
The software does not validate, or incorrectly validates, a certificate. When a certificate is invalid or malicious, it might allow an attacker to spoof a trusted entity by interfering in the communication path between the host and client. The software might connect to a malicious host while believing it is a trusted host, or the software might be deceived into accepting spoofed data that appears to originate from a trusted host.
Products Associated with CVE-2026-40539
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Affected Versions
Synology DiskStation Manager (DSM):- Version 7.3 and below 7.3.2-86009-2 is affected.
- Version 7.2.2 and below 7.2.2-72806-7 is affected.
- Version 7.2.1 and below 7.2.1-69057-10 is affected.
- Before 7.2.1 is unknown.